Abstract: The Nanweixi Basin is a Cenozoic continental margin rift basin in the southern South China Sea. Currently, the in exploration is in early stages and related studies on its source rocks and thermal evolution are nil. Using drilling and integrated geophysical data based on the structural-sedimentary framework, burial history, and paleo-geothermal model, the characteristics and thermal evolution history of source rocks in the basin were investigated. Results indicate that the Oligocene and Lower Miocene argillaceous source rocks and coal-bearing source rocks were developed in the Nanweixi Basin, and the organic matter abundance ranges from moderate to good in mainly types II-III. The Oligocene source rocks are continental lake facies with relatively oxidizing conditions, while the Lower Miocene source rocks are marine-continental transitional facies. The organic matters in both cases are in mixed origin predominantly from terrestrial higher plants. The thermal evolution history study revealed that the primary source rocks in the basin are the Upper Eocene-Lower Oligocene, flowed by the Upper Oligocene. The Lower Miocene source rocks are in low maturity and contributed slightly to the hydrocarbon generation. The thermal evolution degrees of source rocks vary significantly among four main depressions of the basin, of which the northwestern and southern depressions have higher thermal evolution levels. Source rock thickness was estimated using seismic facies analysis and regional analogy. Results suggest that the central part of the Central Depression and northeastern part of the Southern Depression are favorable for source rock development. Integrated assessment of source-reservoir-igneous rock systems indicated that the most promising exploration targets lie in the Southern Depression and the adjacent Southern Uplift.